As next generation lighting devices or display devices, display devices using light-emitting elements (organic EL elements) in which organic compounds are used as light-emitting substances have been developed, announced, and partially commercialized because of their potential for thinness, lightness, high speed response to input signals, low power consumption, and the like.
In an organic EL element, voltage application between electrodes between which a light-emitting layer is provided causes recombination of electrons and holes injected from the electrodes, which brings a light-emitting substance that is an organic compound into an excited state, and the return from the excited state to the ground state is accompanied by light emission. Since the spectrum of light emitted from a light-emitting substance is peculiar to the light-emitting substance, use of different types of organic compounds for light-emitting substances makes it possible to provide light-emitting elements which exhibit various colors.
In the case of light-emitting devices which are expected to display images, such as displays, at least three-color light, i.e., red light, green light, and blue light, is necessary for reproduction of full-color images. Further, to enhance image quality with favorable color reproducibility, various efforts such as use of a microcavity structure and a color filter have been made to improve color purity.
A light-emitting device with lower power consumption due to addition of white light to three-color light (red light, green light, and blue light) has been proposed and commercialized.
There are mainly three methods to realize full-color display using the light-emitting elements described above: so-called side-by-side patterning in which light-emitting elements which emit light of different colors are separately formed; a white-color filter method (white-CF method) in which white color light-emitting element is combined with a color filter; and a color conversion method in which a light-emitting element which emits monochromatic light such as a blue light-emitting element is combined with a color conversion filter. Each of the methods has advantages and disadvantages.